Automatic tool loader for a machine tool

ABSTRACT

An automatic tool loader for a machine tool comprises a magazine containing a plurality of tool holders at respective locations therein, a handling device for removing a required tool holder from the magazine and for supplying the tool holder to a machine tool, the magazine and the handling device being relatively movable to select the required tool holder, the magazine comprising for each tool holder a retaining device which engages and retains the tool holder in the magazine with a limited resiliently biased retaining force which the handling device must overcome to supply the required tool holder to the machine tool, the handling device comprising a connecting device which connects the required tool holder to the handling device with a limited resiliently biased connecting force, said force being sufficient to enable the handling device to supply to tool holder to the machine and to subsequently remove the tool holder from the machine tool when it is released thereby, said force being overcome by the handling device when the tool holder is retained by the machine tool for use or when the tool holder is returned to its location in the magazine, whereby to disconnect the handling device from the tool holder.

United States Patent Chabrier [54] AUTOMATIC TOOL LOADER FOR A MACIMETOOL Primary Examiner-Andrew R. Juhasz Assistant Examiner-Z. R. Bilinsky4 1 Aug. 15,1972

[ TRACT An automatic tool loader for a machine tool comprises a magazinecontaining a plurality of tool holders at respective locations therein,a handling device for removing a required tool holder from the magazineand for supplying the tool holder to a machine tool, the magazine andthe handling device being relatively movable to select the required toolholder, the magazine comprising for each tool holder a retaining devicewhich engages and retains the tool holder in the magazine with a limitedresiliently biased retaining force which the handling device mustovercome to supply the required tool holder to the machine tool, thehandling device comprising a connecting device which connects therequired tool holder to the handling device with a limited resilientlybiased connecting force, said force being sufficient to enable thebandling device to supply to tool holder to the machine and tosubsequently remove the tool holder from the machine tool when it isreleased thereby, said force being overcome by the handling device whenthe tool holder is retained by the machine tool for use or when the toolholder is returned to its location in the magazine, whereby todisconnect the handling device from the tool holder.

Attorney-Delio & Montgomery 6 Claims, 3 Drawing Figures 6 l6 f 22 33I''''"" I ie-3' 121 PATENTEDAUB 15 1912 3. 683.490

lnvenlor Mavl'lal Chobrlev AUTOMATIC TOOL LOADER FOR A MACHINE TOOL Thepresent invention relates to an automatic tool loader for use with amachine tool.

The invention is particularly but not exclusively applicable to anautomatic tool loader for a vertical lathe.

An automatic tool loader generally permits the removal of a tool whichhas completed a phase of the work, its return to the compartment of amagazine to which it is allocated, the selection of the compartment inthe magazine which contains the tool which is to carry out the nextphase, the removal of this tool from the selected compartment, and itsdelivery to the machine tool in a position such that its positioning andfastening can be effected.

The aim of the present invention is to provide a simple, sure, sturdy,effective, reliable, easily manufactured, relatively inexpensive loaderwhich is of small size and can be fitted without substantialmodification to a machine tool.

The present invention also has the object of enabling the operationsindicated above to be carried out rapidly, and above all to achieve veryaccurate and correct positioning and fastening of the tool on theshaping element.

The present invention has another object to allow full freedom ofutilization of the machine for the performance of special jobs or shortproduction runs which do not justify programming, by permitting a loaderaccording to the invention to be easily disconnected from the machinetool thereby permitting and facilitating a manual tool-loadingoperation.

According to the invention, there is provided an automatic tool loaderfor a machine tool, comprising a magazine, -a plurality of tool holdersat respective locations therein, a handling device for removing arequired tool holder from the magazine and for supplying the tool holderto a machine tool, means supporting the magazine and the handling devicefor relative move ment to select the required tool holder, the magazinecomprising for each tool holder a retaining device to engage and retainthe tool holder in the magazine with a limited resiliently biassedretaining force which the handling device must overcome to supply therequired tool holder to the machine tool, the handling device comprisinga connecting device to connect the required tool holder to the handlingdevice with a limited resiliently biassed connecting force, said forcebeing sufficient to enable the handling device to supply the tool holderto the machine and to subsequently remove the tool holder from themachine tool when it is released thereby, said force being overcome bythe handling device when the tool holder is retained by the machine toolfor use or when the tool holder is returned to its location in themagazine, whereby the handling device is disconnected from the toolholder.

The retaining device may comprise a detent, the tool holder having meansdefining a recess therein which is engaged by the detent, a leaf springsupporting the detent from the magazine and resiliently biassing thedetent into the recess.

The recess maybe a notch having a retaining face perpendicular to therelative motion between the tool holder and the magazine which occurswhen the tool holder is supplied to the machine tool, the detent havinga face which engages the retaining face when the detent is in the notch,and is inclined to the retaining face at an angle slightly greater thanthe angle of friction existing between the engaged faces.

The connecting device may comprise a detent, the tool holder havingmeans defining a recess therein which is engaged by the detent, a leafspring supporting the detent from the handling device and resilientlybiassing the detent into the notch.

The last-mentioned recess may be a notch having a retaining faceperpendicular to the relative motion between the tool holder and thehandling device during disconnection thereof, the detent having a facewhich engages the retaining face when the detent is in the notch, and isinclined to the retaining face at an angle slightly greater than theangle of friction existing between the engaged faces.

The retaining device and the connecting device may comprise respectiveleaf springs, at least the leaf spring of the retaining device beingstraight, a semiencastre mounting supporting said leaf spring.

Alternatively, or in addition, a semi-encastre mount ing may be providedat least for the leaf spring of the connecting device, at least thelatter leaf spring being straight except for a bight-shaped curvedportion adjacent the mounting.

The handling device may comprise a forked member, each tool holderhaving shoulders which are engaged by the forked member to support thetool holder.

Each tool holder may comprise inclined surfaces on the shouldersthereof, the fork member having corresponding inclined surfaces whichengage the inclined surfaces on the said shoulders to lift the toolholder.

There may be driving and braking means for moving the magazine relativeto the handling device into approximate alignment therewith forselecting the required tool holder, indexing means for accuratelyaligning the magazine and the handling device for selection of therequired tool holder, and sensing means for sensing movement of thehandling device from a rest position and for releasing the braking meansto permit said accurate alignment by the indexing means.

For each said location of the magazine there may be ftuther sensingmeans for sensing when the magazine and the handling device are in saidapproximate alignment, and for thereupon operating the braking meansuntil the first-mentioned sensing means releases the braking device.

Various other characteristics of the invention will be clear from thedetailed description which follows.

One embodiment of the invention is illustrated by way of non-lirnitativeexample in the accompanying drawings, in which FIG. 1 is a partialdiagrammatic elevation and section of an automatic tool loader accordingto the invention, applied to a vertical lathe;

FIG. 2 is a section on a larger scale in the same plane as FIG. 1 andillustrates the operation of the loader; and

FIG. 3 is a similar view to FIG. 2, showing another phase of theoperation of the loader.

In FIG. 11, reference 1 indicates a tool holder, and a slide of themovable carriage of a vertical lathe is shown at 2. The tool holder isintended to be positioned accurately in relation to the slide 2 and tobe fixed firmly and in a stable manner thereto. In order to achieve thisaccurate positioning and secure fastening, use may be made of variousdevices, particularly that illustrated in FIG. 3. This device is notdescribed in the present application because it is described and claimedin my copending U.S. Patent application No. 41,908 filed June 1, 1970having the title Tool Support for a Machine Tool.

The tool loader of FIG. 1 comprises a fixed frame 3 containing a plate 4fastened to a vertical tubular column 5 and at least one fasteningbracket 6. A cylindrical drum 8 has integral therewith at the top aplate 9 forming a magazine and at the bottom a toothed crownwheel 10.The drum 8 is mounted for rotation around the column 5, for example bymeans of bearings and thrust bearings 7. The plate 4 and the bracket 6support a motor 1 1 which by means of a brake 12 and a clutch 13 iscoupled to a reduction unit 14, the output shaft of which is providedwith a drive pinion 15 meshing with the toothed crownwheel 10. Thisassembly constitutes a driving and braking means for the rotating plateof the magazine 9. In addition, the plate 4 of the fixed frame 3 alsocarries an indexing device 16 constituted by a vertically guided conicalpush-rod 17 connected to an operating element and cooperatingselectively with a number of conical sockets 18 in the magazine 9 equalto the number or compartments or locations in the latter, thesecompartments being described hereinbelow and serving to receive andstore the tool holders 1. The angular distribution of the sockets 18 isthe same as that of the compartments. The operating element of thepush-rod 17 is a ram 19, a piston 20 of which bounds a chamber 21, whichis connected to a pneumatic circuit for effecting the retraction of thepush-rod 17. The piston also bounds a chamber 22 in which there isdisposed a spring 23 acting on said piston in order to effect theengagement of the push-rod 17 in the socket 18 situated opposite it.

The rotating plate 9 has on its periphery a number of cutouts 24,matching the shape of the tool holders 1, the cutouts defining thelocations or compartments of the magazine. Each cutout is open towardsthe periphery of the plate 9 and the side edges of the eutout, which areparallel to one another, are intended to support two shoulders 25situated on each side of the corresponding tool holder 1.

A tool holder handling device comprises a transfer fork 26 situatedabove the rotating plate 9 and guided for translational movement towardsand away from the slide 2; the fork is connected to an operating elementso as to be able to connect with a tool holder which has previously beendisconnected from the slide 2, in order to return it to its position inthe corresponding compartment in the plate 9, which has been previouslybrought into alignment with the fork. The handling device 26 also isable to pick up the next-required tool holder from its magazinecompartment, which previously has been aligned with the fork 26, inorder to supply the tool holder to the slide 2.

The fork 26 is fastened to two pairs of C-shaped ball sockets 27 mountedon two cylindrical guide rods 28 fastened under a bracket 29 integralwith the column 5. The fork 26 is provided with a finger 30 which, inthe rest position of the fork illustrated in FIG. 1, does not contactthe rotating plate 9 but which during the translational movement of thefork is guided in a slot 300, cut radially in the plate 9 and leadinginto each cutout 24. In addition, the fork 26 is coupled by a bar 31a tothe movable part of a ram 31 which forms the aforesaid operating elementand the fixed part of which is carried by the column 5.

The tool holders 1 are supported in various ways during the variousstages of their handling by the tool loader.

When a tool holder is stored in a compartment 24 it rests by itsshoulders 25 on the edges of the cutout in the magazine 9, which formsthe compartment in question (FIG. 1

When a tool holder is situated under the slide 2 and disconnected fromthe latter, it rests by its shoulders 25 on side sections 33 provided onthe slide 2 and constituting guide and support elements (FIG. 1).

When a tool holder is picked up by the fork 26 it rests by its shoulders32, situated above the shoulders 25, on the two prongs of the fork, butit no longer rests either on the rotating plate 9 nor on the sections 33of the slide 2.

To lift the tool holder from the sections 33 of the slide 2, the prongs34 of the fork and the shoulders 32 of each tool holder 1 are providedwith inter-engaging inclined planes 35 and 36 respectively (FIG. 1)which on the application of the fork to the tool holder, effects aslight lifting thereof.

Referring to FIGS. 2 and 3, the handling device has a connecting device37 comprising a detent connected to the fork 26 by at least onecalibrated leaf spring blade 38 and adapted to cooperate with a recessor notch 39 provided in each of the tool holders 1. The notch 39 has aretaining face 39a extending substantially perpendicular to the relativemotion between the handling device and the tool holder upondisconnection of the one from the other. Thus, the face 39a issubstantially vertical. A substantially horizontal cam surface 39b isprovided to deflect the detent 37 prior to engagement with the notch 39.

The detent has a sloping projecting face 37b provided to cooperate witha cam surface 39b, and an inclined face 370 which engages the retainingsurface 39a. The inclination of the face 37a is slightly greater thanthe angle of friction between the surfaces 37a, 39a.

By means of the inclination of the face 37a and by suitable calibrationof the spring 38, a limited connecting force is obtained between a toolholder and the fork 26, this force being sufficient to permit the supplyof the tool holder to the slide 2 by the fork and the subsequent removalof the tool holder to its location in the magazine 9 when it has beenreleased by the machine tool. However, the force is overcome by thehandling device when the tool holder is retained by the machine tool orwhen it is located in the magazine 9, and the tool holder is therebydisconnected from the fork 26.

The leaf spring blade or blades 38 is fixed to the fork 26 by means of ascrew 40, which with the aid of a covering plate 41 provides asemi-encastre mounting. The leaf spring blade or blades 38 are straightover their entire length apart from near the fork, where there is abight-shaped portion 380 which enables the correct spring stiffness tobe obtained.

The magazine is provided with a respective retaining element 42 for eachcompartment 24 thereof. Each retaining element 42 comprises a detentconnected to the rotating plate 9 by at least one calibrated springblade 43 and is adapted to cooperate with a recess or notch 44 providedin each of the tool holders 1. Similarly to the notches 39, each notch44 has a substantially vertical retaining face 44a, perpendicular to themovement of the tool holder relative to the magazine when it is removedtherefrom, and a substan tially horizontal cam surface 44b intended todeflect the detent 42. The detent has a sloping face 42b intended tocooperate with the cam surface 44b, and an inclined face 42a adapted toengage the surface 440. The inclination of the face 42a is slightlygreater than the angle of friction between the surfaces 42a, 44a.

By means of the inclined face 42a and by suitable calibration of thespring blade 43, a limited retaining force is provided to retain thetool holder in its location in the magazine 9. This force is sufficientto retain the tool holder in its location when the fork 36 is engagedaround it, but is insufficient to retain the tool holder when the fork26 positively moves it out of its location by applying its drivingshoulder 45 (FIG. 3) thereto.

The end of the leaf spring blade or blades 43 is fixed to the magazine 9by means of screws 46, which with the aid of a covering plate 47 form asemi-encastre mounting. These blades 43 are straight over their entirelength, and the position of their mounting is adjustable (e. g., bymoving the plate 47) to control the spring stiffness.

The slide 2 determines the limit of the movement of the tool holderselected and transported by the fork. For this purpose, the slide 2 hasan element 18a which engages an adjustable stop 16a with which each toolholder is provided, when the selected tool holder is inserted in theguide sections 33 of the slide.

The tool loader operates in the manner described below.

At the commencement of a cycle, as illustrated in FIG. 1, the toolholder 1 which has just completed a machining operation is disconnectedfrom the slide 2 and rests on the section guides 33 of the latter.Simultaneously with the disconnection of this tool holder, a programmerwhich initiated this operation controls the selection of the compartmentof the magazine 9 in which said tool holder is to be stored. For thispurpose, it connects the chamber 21 of the indexing device to the fluidcircuit and thus retracts the indexing push-rod 17, so that the plate 9becomes free to turn. At the same time it operates the motor 11 andclamps 13 by freeingthe brake 12, in order to rotate the plate 9 withthe aid of the pinion 15 and the crownwheel 10.

The plate 4 of the frame 3 carries as many microswitches (which can beselected by fingers on the toothed crown-wheel 10) as there arecompartments in the magazine 9, these rnicroswitches being connected tothe aforesaid programmer. Furthermore, another microswitch is placed inthe path of the movable assembly comprising the fork 26, so as to beoperated as soon as the latter leaves the rest position illustrated inFIG. 1, this microswitch being in turn connected to the programmer.

The programmer having selected the microswitch on the plate 4 whichcorresponds to the compartment in which the disconnected tool holder 1has to be stored, this microswitch is then operated by the finger of thecrownwheel 10 which is associated with said compartment, and itsimultaneously stops and declutches the motor 11 and clutch 13, and alsooperates the brake 12, which has the effect of stopping the magazine 9with the selected location roughly aligned with the fork 26, so that thespring 23 effects approximate engagement of the conical push-rod 17 inthe socket 18 in the crownwheel 10 which is associated with the selectedlocation.

The programmer then operates the rarn 31 to move the fork 26 towards theslide 2. At the commencement of the movement, the abovementionedmicroswitch in the path of the fork 26 is operated and through themedium of the programmer releases the brake 12.

Then the magazine 9 is free to turn and the springloaded conicalpush-rod 17 completes the alignment thereof by rotating the plate 9 andexactly engaging the socket 18. Thus, the magazine is locked in a veryaccurate position in which the selected compartment is alignedaccurately opposite the tool to be received in it.

The fork 26 then is moved in the direction of the arrow F (FIG. 1) untilit reaches the position shown in FIG. 3. It will be seen that the prongs34 of the fork are engaged over the tool holder 1 which is to bereturned to the compartment and which up to that moment had been restingon the section guides 33. During a first phase of this engagementmovement the inclined planes 35 and 36 of the prongs 34 of the fork andof the shoulders 32 of the tool holder effect a slight raising of thelatter, which now rests only on the aforesaid prongs of the fork. Duringa second phase of this engagement, the sloping face 37b cooperates withthe cam surface 39b to effect the deflection of the spring blade 38 andalso the retraction of the detent 37; this is possible because the toolholder 1 to be returned to the compartment is locked through the contactof its stop 16a against the element 18a on the slide. The detent 37,returned by the blade 38, is urged resiliently into the notch 39 andthen the drive shoulder 45 of the fork strikes against the tool holder.During the return movement, that is to say the movement in the oppositedirection to that of the arrow F, the fork 26, on which the tool holder1 to be returned to the compartment is locked by the detent 37, bringsthe tool holder into the selected compartment 24 in the magazine 9 (FIG.3).

When the tool holder is received in the magazine 9, the sloping face42b, cooperating with the cam surface 44b, deflects the spring blade 43and retracts the detent 42 until the latter engages in the notch 44 onthe tool holder 1. Simultaneously, the tool holder abuts the end of thecutout 24. The fork 26 continues its return movement but, since thereturned tool holder 1 is fully home in the compartment, the detent 37is deflected because the locking force obtained by contact between theface 37a and the shoulder 39a is insufficient to prevent thisdisplacement of the detent 37.

When the fork 26 reaches the end of its movement, as illustrated in FIG.1, the programmer again operates in the manner described hereinabove, soas to bring opposite the slide 2 the compartment 24 containing the nexttool to be supplied to the slide 2 in place of the one which has justbeen returned.

The fork 26 is again displaced in the direction of the arrow F and, asillustrated in FIG. 2, engages over the tool holder 1 to be supplied,raising it slightly through the cooperation of the inclined planes 35and 36. This engagement and also the engagement of the detent 37 in thenotch 39, as already described, are possible because the tool holder tobe mounted is held in the compartment 24 in the magazine 9 by the detent42. The locking force produced through the contact of the face 42a withthe shoulder 44a is suflicient to prevent the tool holder in questionfrom being moved by the fork 26 as a result of friction and thedeflection of the detent 37. As soon as the driving shoulder 45 of thefork comes into contact with the tool holder, the driving howeverbecomes positive and the aforesaid locking force is no longer sufficientto prevent it. Consequently, the detent 42 is deflected and frees thetool holder which is then transported by the fork until its stop 16abears against the element 180.

The mounting of the tool holder in the slide 2 is initiated by theprogrammer and efiected automatically with the aid of a screw 11a and ofa captive nut 6a, as described in our aforementioned copendingapplication. Even before the mounting operation is completed, the fork26 is retracted along its return path in the opposite direction to thatof the arrow F. The detent 37 is easily retracted because the toolholder 1 is locked.

Various modifications may be made to the illustrated embodiment. Inparticular, the magazine 9 may be of a different type, for examplerectilinear and it may perform a reciprocating movement or, for example,move in a closed path comprising straight portions connected bysemicircular portions, with a continuous movement. Similarly, themagazine driving, braking, and indexing device may also be of anothertype utilizing different means, as long as it enables any compartment ofthe magazine to be selected. The curved leaf spring 38 may besubstituted for the straight adjustably mounted leaf spring 42, or viceversa.

What I claim is:

1. An automatic tool loader for a machine tool, comprising a magazine, aplurality of tool holders at respective locations therein, a handlingdevice for removing a required tool holder from the magazine and forsupplying the tool holder to a machine tool, means supporting themagazine and the handling device for relative movement to select therequired tool holder, the magazine comprising for each tool holder aretaining device to engage and retain the tool holder in the magazinewith a limited resiliently biassed retaining force which the handlingdevice must overcome to supply the required tool holder to the machinetool, the

handling device comprising a connecting device to connect the requiredtool holder to the handling device with a limited resiliently biassedconnecting force, said force being sufficient to enable the handlingdevice to supply the tool holder to the machine and to subsequentlyremove the tool holder from the machine tool when it is releasedthereby, said force being overcome by the handling device when the toolholder is retained by the machine tool for use or when the tool holderis returned to its location in the magazine, whereby the handling deviceis disconnected from the tool holder, and wherein said retaining devicecomtaa s ssszaw ttilagsgrwte atttsia spring supporting the detent fromthe magazine and resiliently biasing the detent into the recess.

2. An automatic tool loader as claimed in claim 1 in which the recess isa notch having a retaining face perpendicular to the relative motionbetween the tool holder and the magazine which occurs when the toolholder is supplied to the machine tool, the detent having a face whichengages the retaining face when the detent is in the notch, and isinclined to the retaining face at an angle slightly greater than theangle of friction existing between the engaged faces.

3. An automatic tool loader as claimed in claim 1, wherein theconnecting device comprises a detent, the tool holder having meansdefining a recess therein which is engaged by the detent, a leaf springsupporting the detent from the handling device and resiliently biassingthe detent into the notch.

4. An automatic tool loader as claimed in claim 3 in which the recess isa notch having a retaining face perpendicular to the relative motionbetween the tool holder and the handling device during disconnectionthereof, the detent having a face which engages the retaining face whenthe detent is in the notch, and is inclined to the retaining face at anangle slightly greater than the angle of friction existing between theengaged faces.

5. An automatic tool loader as claimed in claim 1 wherein the handlingdevice comprises a forked member, each tool holder having shoulderswhich are engaged by the forked member to support the tool holder.

6. An automatic tool loader as claimed in claim 5 wherein each toolholder comprises respective inclined surfaces on the shoulders thereof,the fork member having corresponding inclined surfaces which engage theinclined surfaces on the said shoulders to lift the tool holder.

ag UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 4 Patent No.3,683, l9O' Dated "August 15, 19 72 "x g Marti-a1 Chabrier It iscertified that error appears in the above-ideritified patent: and thatsaid Letters Patent are hereby corrected as shown below:

' Title page, fourth line (designation [73]), change C.H.M.P. to readC.N.M.P'.

Signed and sealed this 8th day of May 1973- @LAL) attest:

rpimijlo :TJ gETCHEl-TJR. ROBERT GOTTSCHMK J-L'BtGS ClIIg ulflcenCommissioner of Patents

1. An automatic tool loader for a machine tool, comprising a magazinE, aplurality of tool holders at respective locations therein, a handlingdevice for removing a required tool holder from the magazine and forsupplying the tool holder to a machine tool, means supporting themagazine and the handling device for relative movement to select therequired tool holder, the magazine comprising for each tool holder aretaining device to engage and retain the tool holder in the magazinewith a limited resiliently biassed retaining force which the handlingdevice must overcome to supply the required tool holder to the machinetool, the handling device comprising a connecting device to connect therequired tool holder to the handling device with a limited resilientlybiassed connecting force, said force being sufficient to enable thehandling device to supply the tool holder to the machine and tosubsequently remove the tool holder from the machine tool when it isreleased thereby, said force being overcome by the handling device whenthe tool holder is retained by the machine tool for use or when the toolholder is returned to its location in the magazine, whereby the handlingdevice is disconnected from the tool holder, and wherein said retainingdevice comprises a detent, the tool holder having means defining arecess therein which is engaged by the detent, a leaf spring supportingthe detent from the magazine and resiliently biasing the detent into therecess.
 2. An automatic tool loader as claimed in claim 1 in which therecess is a notch having a retaining face perpendicular to the relativemotion between the tool holder and the magazine which occurs when thetool holder is supplied to the machine tool, the detent having a facewhich engages the retaining face when the detent is in the notch, and isinclined to the retaining face at an angle slightly greater than theangle of friction existing between the engaged faces.
 3. An automatictool loader as claimed in claim 1, wherein the connecting devicecomprises a detent, the tool holder having means defining a recesstherein which is engaged by the detent, a leaf spring supporting thedetent from the handling device and resiliently biassing the detent intothe notch.
 4. An automatic tool loader as claimed in claim 3 in whichthe recess is a notch having a retaining face perpendicular to therelative motion between the tool holder and the handling device duringdisconnection thereof, the detent having a face which engages theretaining face when the detent is in the notch, and is inclined to theretaining face at an angle slightly greater than the angle of frictionexisting between the engaged faces.
 5. An automatic tool loader asclaimed in claim 1 wherein the handling device comprises a forkedmember, each tool holder having shoulders which are engaged by theforked member to support the tool holder.
 6. An automatic tool loader asclaimed in claim 5 wherein each tool holder comprises respectiveinclined surfaces on the shoulders thereof, the fork member havingcorresponding inclined surfaces which engage the inclined surfaces onthe said shoulders to lift the tool holder.